Dientamoeba fragilis

Dientamoeba fragilis is an amoeboflagellate and, though
forming no flagella, is most closely allied with the flagellates. It
is currently placed within the family
Monocercomonadidae. Trophozoites are small, 5-12 micrometers in length,
and 60-80% are binucleate. Good staining reveals a mitotic spindle
interconnecting the two nuclei. No cysts are formed and the parasite is
unable to survive passage through the stomach.

Like most intestinal amoebae (or in this case amoebae-like organism),
Dientamoeba fragilis can cause mild
to moderate diarrhea and abdominal discomfort. However, it is not
known to be invasive like Entamoeba histolytica. Studies have
shown that D. fragilis can survive
in the eggs of the human pinworm, Enterobius vermicularis (1956,
Am. J. Trop. Med. Hyg. 5: 258-265; 1977,
Am. J. Trop. Med. Hyg. 26: 16-22). Thus, like the closely related
Histomonas meleagridis, it is likely that transmission of this
protozoan is also through ingestion of pinworm ova.

One recent study (2000, J Clin Microbiol 38: 4653-4654) has revealed two
distinct genetic variants. These may or may not represent distinct,
morphologically similar species.